There is increased focus on digital imagery of culture plates for detection of microbial growth. Techniques for imaging plates for detecting microbial growth are described in PCT Publication No. WO2015/114121, the entirety of which is incorporated by reference herein. Using such techniques, laboratory staff is no longer required to read plates by direct visual inspection but can use high quality digital images for plate inspection. Shifting laboratory workflow and decision-making to examination of digital images of culture plates can also improve efficiency. Images can be marked by an operator for further work-up by either the operator or another person with the appropriate skills. Additional images may also be taken and used to guide secondary processes.
Detection of colonies, colony enumeration, colony population differentiation and colony identification define the objectives for a modern microbiology imaging system. Having these objectives realized as early as possible achieves the goals of delivering results to a patient quickly and providing such results and analysis economically. Automating laboratory workflow and decision-making can improve the speed and cost at which these goals may be achieved.
Although significant progress has been made regarding imaging technologies for detecting evidence of microbial growth, it is still sought to extend such imaging technologies to support an automated workflow. Apparatus and methods for inspecting culture plates for indications of microbial growth are difficult to automate, due in part to the highly visual nature of plate inspection. In this regard, it is desirable to develop techniques that may automatically interpret culture plate images and determine the next steps to be performed (e.g., identification of colonies, susceptibility testing, etc.) based on the automated interpretation.
For example, counting colonies in a plated culture can be difficult, especially when the colonies are of different size and shape and are touching each other. These problems are exacerbated when growth has already reached confluence in some regions of the plate. For these reasons, it is preferable, if possible, to count CFUs early in the incubation process. However, time for incubation is still needed to allow for at least some growth of the colonies. Thus, on the one hand, the longer that colonies are allowed to grow, the more they begin to contrast with their background and each other, and the easier it becomes to count them. Yet, on the other hand, if the colonies are allowed to grow too long and they begin to fill the plate and/or touch one another, thereby forming confluent regions on the plate, it becomes more difficult to contrast them from one another, making counting more difficult. If one were able to detect colonies at an incubation time when the colonies were still small enough to be isolated from one another despite relatively poor contrast, or if one were able to estimate colony count even when the colonies are large enough to form confluent regions on the plate, this problem could be resolved.